small note:
Dirk must have been blessed with unbelievable number of luck shots and balls flying in his direction, since he could score about 25.700 points & grab 9500 rebounds (reg season + playoffs) despite being such a predictable and one dimensional player.

Durant is great player, but there is nothing special about his play. He is like many other great scorer from the past. He'll have his prime and then decline, because other great scorers will emerge. He isn't MJ.
Dirk in the other hand is very unique. I believe, he could play his game for another 3-4 years and his numbers would decrease only slightly.

and as many have said: no one can guard dirk.

Yep, there have been a lot of 7' small forwards with the handle/shot of a guard in the past